At present, alkaline manganese cells are now in main use as an alkaline primary cell having high output characteristics, in which manganese dioxide is used as a positive electrode active material and zinc is used as a negative electrode active material, with an alkaline aqueous solution being employed as an electrolytic solution. In recent years, as portable appliances including digital cameras, information communication terminals and the like are becoming high in performance, there is an increasing demand for further improvement in high load characteristics and also for high capacity in respect to alkaline manganese cells which are used as a power source.
As a means which is capable of providing a cell having excellent output characteristics in order to meet such a demand as mentioned above, attention has been long paid to application of nickel oxyhydroxide as a positive electrode active material, and studies have been, in fact, made thereon (see Japanese Patent Application Laid-open Publication Nos. Sho 53-32347 and Sho 55-30133).
However, hitherto studied cells using nickel oxyhydroxide as a positive electrode active material have the problem that when the cells are left over a long time under high temperature conditions, the cell capacity decreases owing to self-discharge thereof, and thus have never been put into practice. In particular, with primary cells, the reduction in capacity resulting from self-discharge means a loss of function as a cell. Thus, it is essential to overcome the problem on the reduction of capacity ascribed to self-discharge in order to realize the practical use.